Channel culture devices, of the type which provide multiple plant growth channels of indefinite length but of shallow depth and narrow individual width, have enormous potential value for increasing the world's food supply. They provide maximum plant production for a given supply of fertile soil, water, fertilizer, and other support chemicals, some or all of which are scarce and at an extreme premium in many parts of the world. The growth channels have a limited cross-sectional area that can be made just sufficient for the full root development of any specified plant, so that optimum availability of nutrients and water to the plants is obtained. Further, the isolation of the channels prevents the leaching and escape of the available supply of nutrients and water into the underlying soil. Isolation also simplifies the problems of cultivation, and of the control of pests, disease, and weeds.
One difficulty that has confronted the wider use of channel culture devices has been the cost, and in many needful parts of the world the scarcity, of materials and labor for their construction. Various design proposals have been made, of which some are disclosed and claimed in my copending U.S. Patent Applications Ser. No. 512,518, filed on Oct. 7, 1974, and Ser. No. 625,254, U.S. Pat. No. 3,987,585, filed on Oct. 23, 1975. Such a structure should be easy to set up quickly without skilled labor, should require only locally-available materials or light-weight materials easy to transport, and should be as cheap as possible. At the same time, the device must have structural stability so that it will not collapse under the weight of soil and water it contains.
The foregoing copending applications presented satisfactory alternative solutions for many situations, provided that there is a sufficient and fairly uniform water supply available. However, where this essential element is in limited or irregular supply, as is true in many parts of the world, there is a need for a channel culture device that is capable of storing excess moisture and making it available to the plants in arid periods; and it is an object of this invention to provide such a device. It is a further object to provide an improved channel culture device which has adjacent channels adapted to different but complementary uses. It is another object to provide an improved channel culture device which has the desirable qualities of low cost, ease of assembly and transport, and adaptability to construction from locally-available materials, but which also has an increased ability to store a reserve supply of moisture and to make it available to plants as needed. Further objects and advantages of the invention will appear as the following description proceeds.
Briefly stated, my invention is based in part on the use of a channel element or module which has a horizontal base wall joining two side walls which project upwardly at acute angles so that they are inclined toward one another. These walls form a channel with an open top narrower than the bottom wall; this may be referred to herein as a trapezoidal channel. By placing two or more such channel modules in edge-to-edge relationship, I create V-shaped or triangularsection channels between them, with walls meeting at the bottom and diverging to an open top. A series of the modules are aligned end-to-end to extend both series of channels continuously to any desired length. Because the trapezoidal channels have a small ratio of mouth area to volume, thus reducing the percentage of evaporation loss, they are employed basically as storage channels for moisture, and may serve other support purposes which will appear; while the triangular channels are used as growth channels for receiving the principal plants to be grown in the device.
The side walls of the modules are perforated so that moisture can leach at a limited rate from the trapezoidal storage channels into the triangular growth channels. Plant rootlets may also pass from the growth channels into the storage channels through these perforations to reach areas of high moisture content.
In general, the trapezoidal storage channels are filled with materials principally characterized by good moisture storage capacity, such as gravel, sand, compost, or soil mixed with vermiculite, perlite, peat moss, hydrophilic polymer foams, or nitrile starch. The triangular growth channels may be filled with soil or other known growth medium, to which suitable quantities of fertilizer and other known plant support materials may be added with a minimum of loss by escape into the material in the storage channels. The latter may serve additional purposes, such as to serve for growing an auxiliary or companion crop, e.g. soybeans or alfalfa, which can thereby furnish nitrogen to the primary crop.
I may optionally place inserts of various forms in the trapezoidal channels to subdivide them into growth, storage, or drainage sub-channels, as will appear in the detailed description which follows.